If you dig through your nearest toy box, you’ll find some pretty familiar forms of ancient
life.You got your Triceratops, your Tyrannosaur, and one of my personal favorites, the Pachycephalosaurus
But you know one animal in here that doesn’t quite belong? The one that’s doing its own
thing? The stegosaurus.
If you take it as a given that extinct dinosaurs were all weird and wonderful, then you gotta
at least consider that Stegosaurus was one of the weirdest and wonderfulest.
Stegosaurus is the most recognizable genus of the stegosaurids, four-legged herbivores
that sported bony plates and spiky spines on their backs, earning them the name that
means “roofed lizard.”
But unlike the other dinosaurs you find in the toy box which lived in Cretaceous
Period, stegosaurids hit their prime much earlier, in the Jurassic. This is when some
of the largest herbivores, like Diplodocus, roamed the Earth, while carnivores, like Allosaurus,
had just come on the scene.
It was in this environment that Stegosaurus thrived, with the help of some awesome adaptations.
But in some ways, despite all that armor, it might have been under-equipped. Because
its brain was almost impossibly small.
Stegosaurus had the one of the lowest brain-to-body ratios of any known dinosaur. The animal itself
could grow up to 9 meters long -- about the size of a small bus -- but its brain was only
about 60 square centimeters, the size of a puppy’s.
And when I say that this was almost “impossibly small,” what I mean is, for a century or
so, some paleontologists actually thought that stegosaurus must’ve had a second
brain … ...iiiin its butt.
In the 1880s, Yale paleontologist O. C. Marsh found that some specimens of Stegosaurus had
a big cavity in it sacrum, where the spinal column meets the pelvis.
And he figured, since the brain in the head probably wasn’t doing very much, maybe Stegosaurus
was getting some help from its -- for lack of a better word -- butt-brain.
This led to a pernicious myth that Stegosaurus had, if not an actual second brain, at least
a separate bundle of nervous tissue that helped control its tail and legs.
We know now, of course, that Stegosaurus didn’t have two brains. And some experts think
that cavity in its sacrum was actually used to store glycogen, the starchy compound that
animals -- including you and me -- use to store energy.
And just because its brain was small, that doesn’t mean Stegosaurus was stupid. In
fact, you didn't want to tangle with this thing. Because:
It had a secret weapon: the thagomizer.
That’s the unofficial name for the dinosaur’s spiky tail.
Not all stegosaurids had thagomizers, but for those that did, like Stegosaurus and Kentrosaurus,
fossil evidence suggests they were verrry effective weapons.
In 2014, the study of an Allosaurus fossil from Wyoming showed that its pubic bone had
a puncture wound that matched the spikes on a stegosaur’s tail.
Researchers concluded that the Allosaurus had attacked a Stegosaurus, which landed a
blow right in the predator’s groin. The wound became so badly infected that it killed
the Allosaurus, and the fossil record preserved what’s probably the most gruesome groin shot
ever documented.
Now, I’m sure you’re wondering about the thagomizer’s name.
Well, in 1982, Gary Larson's comic strip The Far Side
depicted a group of cavemen getting a lesson in dinosaur anatomy. And it shows
the weaponized tail of the stegosaurus, labelled as a “thagomizer,” quote, “after the
late Thag Simmons.”
Ok I know what you're going to say, cavemen and dinosaurs did not live at the same time,
but the point is, the name stuck. By the
1990s, paleontologists actually started referring to this tail feature as a thagomizer.
And when I interviewed Dr. Robert Bakker, the researcher who studied the Wyoming Allosaurus,
he assured me that thagomizer is an accepted term for a stegosaurid’s spiky tail.
Now, by far the most recognizable parts of a stegosaurid are the bony plates along its
back, often called scutes.
Not "scutes" by the way, I looked it up...scutes
And if you want to start a real, brawl among a bunch of paleontologists, just ask
them what those scutes were for.
Because, they are still some of the most hotly debated features in dinosaur physiology.
For a long time, it was argued that the scutes were there for thermoregulation.
In the 1970s, researchers found tubes running through some fossilized scutes, and thought
that they may have circulated blood through the plates to radiate heat.
But not everyone agrees with this. Some experts have pointed out that not all stegosaurids
have a full array of scutes, so if they did give them some advantage,
they would be more common.
Others have noted that the tubes don’t actually run all the way through the plates, which
they would do, if their job was to circulate blood.
Now you might also think that the scutes were defensive. But if that were the
case, some experts have asked why they only appear along the back, and not on the sides
or the skull?
The most recent theory is that stegosaurs had scutes because … they just looked awesome.
After all, modern-day birds have made a very good living by having lots of features that
are just for display. So why couldn’t the same have been true for extinct dinosaurs?
In 2005, a paper from Berkeley suggested that the plates helped the dinosaurs tell one species
from another.
Ten years later, another study from Princeton proposed that the plates were even sex-specific,
with females having tall, skinny plates, while males sported bigger, broader ones.
But, again, not everyone agrees.
What I think everyone can agree on is that stegosaurids are famous for good reason.
They might not have had the biggest brains, but they cut a distinctive figure back in
the Jurassic, with their scutes and their spiky tails, which they knew how
to use.
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